Relaxation of Levitation Force of a Stack of HTS Tapes

Nowadays, magnetic bearings are used to design motors, generators, separating platforms, and flywheel energy storage systems. High-temperature superconducting (HTS) magnetic bearing construction is based on YBa
₂
Cu
₃
O
_7-x
(YBCO) bulks through its ability to capture and hold significant magnetic field for a long time. However, that material requires external mechanical reinforcement and has low thermal conductivity, which provides additional restrictions on practical application. Modern HTS tapes do not have such disadvantages. Its structure provides better rigidity and thermal stability in comparison with HTS bulk. One more significant advantage of tapes is simplicity of cutting to required form. In order to construct magnetic bearings from stacks of HTS tapes, it is necessary to have data about stability of system stack magnet under different dynamic processes. In this work, relaxation of levitation force was researched in both static and vibration modes with vertical oscillation frequencies of 15, 20, and 30 Hz. The measurements were performed for stacks with different amounts of 12 mm × 12 mm REBCO tapes in a stack (n = 1, 5, 10, 15, 20) at temperature T = 77 K. Stacks were placed over permanent magnet with a minimal gap of 4 mm. FC cooling method was realized. All static and dynamic relaxation measurements were carried out at 11.6-mm gap.